Enzyme histochemistry in muscle and nerve biopsies is carried out for diagnostic purposes in patients with several neuromuscular disorders. Immunocytochemical studies are conducted using specific antibodies to thymic peptides, to investigate changes in the distribution of epithelial cells and thymocytes in the thymus of patients with myasthenia gravis. Using the cytofluorograph, specific subsets of lymphocytes that carry thymic markers are now being defined. The immunoglobulin of certain patients with paraproteinemic polyneuropathies has been identified as a specific antibody to myelin associated glycoprotein; nerve biopsies from these patients are studied by electron microscopy and immunocytochemically with specific antimyelin antibodies. Serum from patients with demyelinating polyneuropathies is tested in cultures of human Schwann cells for cytotoxicity and specific binding. Because muscle and nerves are involved in antigen-antibody immune reactions, the presence of Fc receptors for IgG and complement in fresh muscle and nerve tissues is being examined. Immune cellular markers during evolution of EAN and EAE induced in monkeys are being investigated and therapies are planned using some novel immunomodulating agents.